JP-2010-285918A (US 2010/0313835) describes a valve timing controller including a housing rotated with a crankshaft and a vane rotor rotated with a camshaft. The vane rotor partitions an inside space of the housing into an advance chamber and a retard chamber in a rotation direction, and working fluid is introduced into the advance chamber or the retard chamber, so that a rotation phase of the vane rotor is changed relative to the housing on the advance side or the retard side.
The valve timing controller has a control valve and a linear solenoid. The control valve controls a flow of the working fluid relative to the advance chamber and the retard chamber by reciprocating a spool in a sleeve in an axial direction. The linear solenoid drives the spool to reciprocate in the axial direction.
JP-2005-45217A (US 2004/0257185) describes such a linear solenoid, in which a magnetic flux generated by a coil passes through a movable core and a fixed core, thereby reciprocating an output shaft in an axial direction together with the movable core. Here, in JP-2010-285918A, the spool is pressingly contact with the output shaft because the spool is biased toward the output shaft by a spring, so the spool can quickly move by following the reciprocation of the output shaft.
In JP-2005-45217A, if a side force is generated to draw the movable core toward the fixed core located on the outer circumference side of the movable core in a radial direction, a movable body integrally constructed by the movable core and the output shaft is pressed against a bearing which supports the movable body from the outer circumference side. At this time, in JP-2010-285918A, the spool may rotate with an interlocking rotor constructed by a vane rotor and a camshaft, and the rotation torque is transmitted to the output shaft from the spool.
In JP-2010-285918A, a sphere-shaped end face of the spool coaxially contacts with a flat end surface of the output shaft, which is perpendicular to the axial direction. In this case, the sphere-shaped end face of the spool and the flat end surface of the output shaft slip with each other, and the transmission of the rotation torque from the spool to the movable body may become intermittent. When the rotation torque is not transmitted from the spool to the output shaft, the movable body starts to reciprocate in the axial direction from the static-friction state, so the friction resistance becomes large between the movable body and the bearing.
If the friction resistance is varied, hysteresis produced between a forward movement and a backward movement of the reciprocation may be increased in the movable body. Further, a stick slip may be caused, so that the reciprocation of the movable body may become intermittent. The hysteresis and the stick slip may lower the control performance of the spool of the control valve which is driven by the movable body.